The present invention relates to a polarizer which exhibits high brightness, a method for manufacturing the polarizer, and an apparatus for display using the polarizer.
In an apparatus for liquid crystal display of the prior art, a polarizing plate having dichromatic absorption of light (dichromatic polarizer) has been used as an element for polarizing light. The polarized light described above can be obtained by transmission and absorption respectively of two kinds of polarized light which cross over each other at a right angle when unpolarized external light is incident on the polarizing plate and transmitted. But by the method described above, as one of the polarized components is absorbed, more than half of the light becomes discarded. Accordingly, substantial light transmittance of polarizing plate which is generally used generally at the present is about 40%, and such a polarizing plate is a problematic area in optical apparatus for which brightness is required.
Further, for obtaining a display of high contrast by increasing the degree of polarization (degree of polarizing) of the dichromatic polarizing plate, it is necessary to concurrently increase a light absorbing fraction, and light transmittance of the polarizing plate which is used in a current apparatus for display of high contrast has a tendency to decrease more. This tendency is especially remarkable in a color display. Therefore, it is the present status that a polarizing plate having low light transmittance must be used in order to increase the saturation of color.
As one way to reduce the light loss a low as possible, for instance, a method which reduces the light loss caused by reflection by decreasing the number of boundaries using concurrently the polarizing plate as one of the substrates of liquid crystal cells has been proposed (JP-A-61-221728 (1986)).
Also, a proposal to reduce the light loss is by a method in which, after transmitting light and reflecting light are separated in linear polarized beams which cross over each other at a right angle by a beam splitter, both of the light beams are made to have the same polarized light by transmitting the beams through a half wave length plate and are made parallel by reflecting with a mirror. Consequently, the degree of polarization is increased without the accompanying phenomenon of light absorption (JP-A-2-69715 (1990)).
As far as using the dichromatic polarizing plate in practical use at the present, the loss of light at the polarizing plate can not be depressed and, accordingly, various kinds of problems are generated.
For instance, with an reflecting type apparatus for liquid crystal display which utilizes natural light, there is a problem that the display of white is not obtainable and only gray is obtainable due to the loss of light at the polarizing plate even though the display is made brighter. On the other hand, with an transmitting type apparatus for liquid crystal display which has a light source, there are problems including that an increment of illuminance in order to obtain enough brightness is accompanied by an increment of consuming power and heat generation. These problems are especially severe in an apparatus for color display which requires a color filter.
The method which is disclosed in JP-A-2-69715 (1990) requires optical members such as a beam splitter and a reflecting mirror etc., and it is difficult to obtain a light source having a large area in spite of enlarging of the apparatus. For instance, it is difficult to use as a back light for an apparatus for liquid crystal display of A5 size. The difficulty is same for both the direct viewing type and the reflecting type.
The first object of the present invention is to provide a polarizer having high optical transmittance, a large area, and a thin thickness by decreasing dichromatic absorption which is a main cause of light loss of such optical members as an apparatus for liquid crystal display.
The second object of the present invention is to provide a method for manufacturing the polarizer.
The third object of the present invention is to provide an apparatus for bright liquid crystal display.
The fourth object of the present invention is to provide a polarizer and an apparatus for liquid crystal display which exhibit improved brightness without lowering display contrast.
The fifth object of the present invention is to provide a polarized light source which uses a polarizer having high optical transmittance by decreasing optical absorption of a polarizing plate in the polarizer and which can be enlarged to a large area.
Further, the sixth object of the present invention is to provide an apparatus for display using the polarized light source described above.